1. Field of the Invention
The present invention relates to dielectric antennas and particularly to a solid dielectric antenna which provides an omni-directional radiation pattern.
2. Description of the Prior Art
Recent developments in millimeter wave systems using integrated circuit technology have included new dielectric waveguides which can be made to have lower losses than metallic types so that the size, weight and cost of such systems can be greatly reduced. Dielectric antenna structures have also been investigated to match the dielectric waveguides. Examples of such structures are found in a paper entitled "Design of Dielectric Grating Antennas for Millimeter-Wave Applications" published in the IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-31, No. 2, February 1983, authored by the present inventors. These rectangular longitudinal corrugated dielectric antennas have provided highly directive small beamwidth radiation patterns. Transitions between antenna and waveguide sections have been made gradual by tapering the depth of corrugations, and tapering the radiating rod end has been used to increase the gain of a dielectric end-fire antenna.
There is a need, however, for dielectric antennas which are omni-directional and provide a circular symmetrical radiation pattern for use in such applications as ground radio communications between moving vehicles and for short range secure communications. A previous related antenna having circumferential grooves on a rod extending from a waveguide is described in another paper entitled "A Millimeter Wave Receiving Antenna with an Omnidirectional or Directional Scannable Azimuth Pattern and a Directional Vertical Pattern" in the IEEE Transactions on Antennas and Propagation, July 1972, by Fred R. Ore. This device, however, had undesired reflections and losses, did not have a tapered radiating section of at least one wavelength long to reduce these effects and required a conductive coating.